A known apparatus and method for determining a seat occupancy is disclosed in JP2009-46093A, in which load sensors are arranged between a cushion portion of a vehicle front passenger seat and a vehicle floor, and a seat occupancy on the vehicle seat is determined on the basis of the sum of loads, detected by the load sensors. Side leg portions are provided at four corners of a lower portion of the seat cushion portion, respectively. The seat cushion portion is engaged with seat rails at the side leg portions so as to be movable relative to the seat rails. The load sensors are provided to the side leg portions, respectively. The load sensors detect loads, applied to the corresponding side leg portions. A seat occupancy determining portion compares the sum of the loads, detected by the load sensors, with a predetermined threshold value, thereby determining the seat occupancy by a passenger on the vehicle seat.
The seat occupancy, which is determined by the apparatus for determining seat occupancy, is used to control an operation of an air-bag. More specifically, in a case where it is determined that an adult is seated on the vehicle seat, the air-bag is controlled so as to be fully deployable. On the other hand, in a case where it is determined that a passenger is not seated on the vehicle seat or that a child is seated on a child seat being fixed to the vehicle seat, the air-bag is controlled so as not to be deployable.
However, simply determining the seat occupancy on the vehicle seat on the basis of the sum of loads, applied to the vehicle seat, may lead to a drawback. For example, a large load may be temporarily applied to the seat cushion portion when a seatbelt is fastened relative to the child seat so as to mount the child seat on the vehicle seat. More specifically, when the child seat is placed on the vehicle seat and a tongue of the seatbelt is engaged with the buckle of the seatbelt, a large load is temporary applied to the seat cushion portion by a user via the buckle. When the loads, applied to the seat cushion portion, is a threshold value or larger, it may be mistakenly determined that an adult is seated on the vehicle seat.
Such drawback may be more likely to occur when the number of the load sensors, provided at the seat cushion portion, is reduced in view of cost reduction for the vehicle seat. In other words, it may be difficult to achieve the accurate determination of the seat occupancy of the vehicle seat and reduction of cost of the vehicle seat at the same time.
A need thus exists for an apparatus and method for determining seat occupancy, which is not susceptible to the drawback mentioned above.